Scientists and explorers will brave polar bears, thin ice and frostbite within the next fortnight as they embark on an Arctic expedition to examine the impact of an acidifying ocean on the region's animals and plants.

The Catlin Arctic Survey will set up an "ice base" in northern Canada for the scientists while a separate team of adventurers will undertake a 500km trek across sea ice off Greenland. Both will investigate the impact of ocean acidification on marine life, while the explorers will also measure variations in sea ice thickness. Last year's Catlin Arctic Survey showed the Arctic ice was thinner than expected.

The expedition will also be the first to take water samples from the sea ice in winter, as all previous Arctic measurements have been taken from ships in open water in summer.

As well as taking water samples, the scientists will collect plankton, sea butterflies, a type of swimming sea snail, and other local marine life and examine their reaction to increasing levels of acidity and also test how much CO2 passes through sea ice from the air into the sea.

Globally, oceans have seen an 30% increase in acidity on pre-industrial levels, the fastest rate of change in 55 million years. The Catlin scientists aim to establish the acidity of the Arctic ocean, which appears to be acidifying faster than the rest of the world's oceans because cold water absorbs more CO2.

Marine life that depends on calcification such as coral, crustacea and molluscs are particularly sensitive to changes in acidity because the calcium carbonate that form their shells or skeletons dissolves in more acidic water. A type of snail known commonly as sea butterflies (pteropods), which are an important part of the marine food chain, are among the organisms potentially at risk.

Pen Hadow, the director of the survey who also led last year's expedition, said the Arctic ocean's vulnerability motivated the trip. "We know that disappearing ice cover and the potential impacts of acidity are parts of some big ocean changes. Since ocean acidification is widely viewed as a bellwether for wider global change, it is important we understand better what is happening."

The ice base on the western shore of Ellef Rignes Island in Canada will be home to a team of six scientists who will work on the ice protected by two guides armed with guns and bangers to ward off curious polar bears attracted by the smell of humans. They will also face hazards such as breaking ice and the risk of frostbite as they undertake the fiddly work of drilling for water samples.

Helen Findlay of Plymouth Marine Laboratory, one of the international team heading to the base, admitted that although she had been to the Arctic before, she had never been in winter. "It's a challenging place to carry out science, though I've been too busy preparing to be nervous," she said.

The three-strong team of explorers led by Ann Daniels, who took part in last year's survey, will face even more extreme conditions with wind-chill bringing temperatures down to -75C. An analysis of the data collected will be published in late 2010 or 2011.

• See G2 on Friday to read Steven Morris' account of the explorers training for the cold on Dartmoor